Aerobic wastewater treatment, especially for industrial, municipal and agricultural wastewaters, bioconverts organocarbons and ammonium cation (the term ammonium cation as used herein encompasses both ammonium cation and dissolved ammonia in the wastewater). The component or components being bioconverted in an aerobic wastewater treatment process are referred to herein as substrate. The oxygen for the bioconversion is supplied by air, oxygen enriched air or pure oxygen. In some facilities, the oxygen-containing gas is bubbled through a bioreactor containing the wastewater. Mass transfer of oxygen to the wastewater occurs from the bubbles, and the bubbles also agitate the wastewater in the bioreactor. The treated water is conventionally subjected to a solids separation unit operation, e.g., a clarifier, to provide a clear water stream and a sludge. The types of processes are characterized as attached growth (static fixed film or dynamic fixed film) or suspended growth using activated sludge.
The aerobic digestion is usually effected by indigenous microorganisms in recycled sludge (activated sludge). These microorganisms may be in the water to be treated and are sometimes supplied externally, and are usually wild-type (naturally-occurring) microorganisms. The relative amount of sludge recycled is subject to practical limitations. For instance, since in suspended growth the microorganisms are typically dispersed in the wastewater as substantially free cells and agglomerates of cells, cell density must be maintained at concentrations below those which result in the wastewater having unduly high viscosities. High viscosities not only adversely affect agitation and transfer of oxygen to the wastewater but also adversely affect the solids separation unit operation. Moreover, at higher cell densities, the cells tend to form more agglomerates which limit the mass transfer of oxygen and substrate to the cells located within the agglomerates. Hence, there is a practical limitation as to the rate of aerobic digestion per unit volume of bioreactor (bioreactor bioactivity).
Moving bed biofilm reactors are one type of attached growth bioreactors for wastewater treatment. These systems use polyethylene, or other polymeric, carrier elements upon which bacteria are attached on the surfaces thereby enabling a higher cell density than can be achieved in a freely suspended cell system. The benefit from the higher concentration of microorganisms is the ability to have higher throughput for a given bioreactor volume, i.e., a higher bioactivity density. Also, in some instances, the recycling of sludge is not required although sludge is generated and requires handling and disposal. These bioreactors are able to achieve bioreactor bioactivities greater than those of activated sludge systems. However, the mass of the biofilms is limited by the available surface area of the carrier, and the densities of the biofilms limit the ability for passage of fluid to internally located microorganisms. Consequently, moving bed biofilm reactors also have restrictions to achieving high bioreactor bioactivity densities.
These aerobic wastewater treatment processes generate sludge. The sludge comprises live and dead microorganisms and their debris and other solids which may have been contained in the wastewater or may be the product of a bioconversion. Frequently about 20 to 50 percent of the carbon and oxygen consumed during the bioconversion is for growth of the population of the microorganisms, and in a steady-state process, a mass substantially equivalent to the amount of this growth will be contained in the sludge. Hence, the volumes of sludge generated can be significant. The sludge separation unit operation is often a bottleneck, especially where the sludge separation is effected by a gravity separation. The sludge has to be disposed in a suitable manner, which can be more problematic if the sludge contains toxic or other environmentally undesired components.
In some wastewater treatment facilities, such as municipal wastewater treatment facilities, the influx of wastewater can vary substantially depending upon the time of day and external factors such as the occurrence of rain or snow melt. Although facilities are typically designed for peak wastewater flows, periods can exist where flows exceed the capacity of the facility. Moreover, an increasing population of users for a given wastewater treatment facility can lead to exceeding the design capacity of the facility, especially during periods of peak wastewater flow to the facility. The facility is faced with a couple of alternatives if it does not expand its capacity. First, discharge of untreated wastewater, and second, retention basins can be used to hold the wastewater until the facility can process the excess wastewater.
Shirazi, et al., in United States published patent application 20130337518 disclose biocatalysts having:                i. a solid structure of hydrated hydrophilic polymer defining an interior structure having a plurality of interconnected major cavities having a smallest dimension of between about 5 and 100 microns and an HEV of at least about 1000 and        ii. a population of microorganisms substantially irreversibly retained in the interior of the solid structure, said population of microorganisms being in a concentration of at least about 60 grams per liter based upon the volume defined by the exterior of the solid structure when fully hydrated,wherein the microorganisms maintain their population substantially stable. The irreversibly retained microorganisms are believed to undergo phenotypic alterations. Moreover, the biocatalyst has a long lifetime and competition with undesired microorganism is substantially eliminated. For ease of reference, these biocatalysts are herein referred to as ME biocatalysts. The ME biocatalysts have been proposed for many processes including, but not limited to, wastewater treatment such as aerobic digestion, anaerobic digestion, phosphorus removal, metal removals, nitrification, and denitrification.        